Tag Support for Subnets

[andrewgross]

Most of the sample AWS responses have empty tags, it would be nice to bolster these by adding some tags and update the templates to include them. Normally moto returns <tagSet/> as that is the default. However, the tags can be properly mocked out with something similar to

<tagSet>
    <item>
        <key>Tag1</key>
        <value>Foo</value>
    </item>
    <item>
        <key>MyName</key>
        <value>Bar</value>
    </item>
</tagSet>

I will see what I can do to add this to a PR.

[spulec]

Agreed that it would be great to have this.